CoPt nanoparticles by a modified polyol process

We synthesized monodisperse CoPt nanoparticles by a modified polyol process, in which Co(acac)3 and Pt(acac)2 were co-reduced by a diol in the presence of PVP surfactants at high temperature (acac = acetylacetonate, PVP = polyvinylpyrrolidone). It is found that the CoPt nanoparticles assume a face-centered cubic phase and possess high crystallinity, with a particle size of 5.3 nm and a tight size distribution. The nanoparticles show superparamagnetism in the as-synthesized state and become ferromagnetic after annealing. The magnetization process of the nanoparticles prior to heat treatment was analyzed by the Langevin equation and their effective magnetic particle size was thus obtained, in close approximation to the results from the XRD and TEM observation.